"In the specific case of WMT the other verses set a bit of a pattern" - No: they come after the non-rhyming verse, so the pattern hasn't been set when the non-rhyme occurs.

Put me in the camp of those who didn't notice the lack of a rhyme until they read this thread.

To my ear, the bit with 'perfuming' seems just a little too, um - "poetic", whereas "all around the blooming heather" is closer to English as she's spoke.

Someone above was mocking 'tower' for 'bower' - I have a book of Clancy Bros. lyrics that has 'tower' .....